1. Field of the Invention
This invention relates to a barrier assembly mounted in an offshore disposition within a body of water by anchoring the barrier to the floor or bottom and structuring the barrier assembly to intercept inflowing waves of a variety of strength thereby dissipating the force of such waves before the waves can derogatorily affect the sand on or about the shoreline which normally causes erosion.
2. Description of the Prior Art
Numerous prior art structures and devices have been devised to reduce or eliminate the tendency for beach or shoreline erosion caused by waves varying in strength from generally normal continuous wave action to storm or hurricane level. Certain existing publications in the United States have emphasized the importance of conservation of the nation's shoreline as indicated hereinafter.
Science Digest, August 1986 Volume, "America Washing Away" indicates that the sea level throughout the world is rising from a negligible six inches over the past century to a possible one foot or more within the next fifty years. Each foot of sea level rise can destroy from approximately one hundred to many thousand feet of coastline. The forces responsible for such erosion are beyond anyone's control as well as general scientific understanding. Within the next ten years, homes in every coastal town and on every barrier island will be at risk of being destroyed if hurricanes or storms of sufficient strength occur.
It is also well known that the abnormal rising of sea level could very well be attributed to "global warming" which according to many prestigious and nationally sponsored societies may well be the most pressing international issue of the next century.
Storm surges and high tides could flood hundreds of abandoned toxic waste sites located near the coasts thereby directly threatening human health by contaminating ground water.
Cities such as Miami Beach, Fla.; Ocean City, N.J.; East Hampton, N.Y. and Malibu, Calif. have attempted to stop such derogatory effects on the adjacent shorelines by building walls in front of the beach area to hold back the sea. Additional efforts include the creation of jetties to stabilize inlets and the establishment of stone groins that extend perpendicular outward from the beaches into the water for the purpose of trapping sand. In many cases, these structures have accomplished the opposite of that intended and have in fact hastened erosion.
The only way to widened or re-establish a beach uniformly and protect all of the contiguous property is to replenish such beach or coastline with new sand. Importing and is prohibitably expensive to all but the wealthiest resorts and individuals.
In the July 1987 issue of Scientific American and article entitled "Beach and Barrier Islands" indicated that one of the world's most spectacular sand beaches runs from the New England area of the North American continent down the Atlantic coast of the United States and travels continuously around the State of Florida to extend along the northern edge of the Gulf of Mexico. Much of the 2,700 mile beach lies on the 295 "barrier islands" that stand between the sea and the mainland along the two coasts. Both the mainland beaches and the islands are under constant attack from the sea. Today, such resorts, of the type mentioned above, occupy barrier islands and summer homes crowd many of such beaches. Naturally, pressure for pubic works to protect the islands and beaches is strong. It is impossible for a large storm of hurricane strength to move along either coast without either crossing or at least affecting a beach or barrier island. Hurricanes are more powerful than storms known as Winter Northeasters, but they come less often, particularly along the Atlantic coast. There are roughly thirty occurrences wherein Northeasters generate waves with sufficient force to erode the barrier island beaches and frontal dunes.
The overall shoreline erosion along the mid-Atlantic coast is from 1.5 to 4.5 feet per year. This does not apply to the barrier islands off the Virginia coast and the beaches along the Delta coast of Louisiana. There the erosion rate can be as much as 25 feet per year.
The aforementioned article additionally sets forth that in 1946, Congress first authorized the expenditure of federal funds to build structures to prevent erosion. Under that authority, the Army Corps of engineers built more than a hundred projects. These projects encompass both "hard" structures and "soft" engineering works. The hard structures include breakwaters, groins, sea walls and revetments. The latter structure, a revetment is built on the beach to prevent waves from removing sand. Experience has learned that manmade structures of the type set forth above have not only failed to protect the beaches and shorelines but in many cases, have actually worked to destroy them. The trend in coastal engineering today is to take the soft approach. This technique entails adding sand to a beach to replace material lost by natural erosion.
The continuing rise in sea level and encroachment on the shoreline will challenge engineers seeking to maintain the resort communities built on beaches and barrier islands. If the predicted increase in atmospheric carbon dioxide from the burning of fossil fuels brings about a global warming and increased melting of polar ice, th e sea level will rise even faster and shoreline recession will accelerate.
The articles described the deteriorating condition of the American beaches and the resulting hazardous situation involving coastal residential constructions. The Conservation Foundation for the Counsel on Environmental Quality, the Departments of Commerce, Defense, Interior, Environmental Protection Agency and the Federal Emergency Management Agency have prepared guidelines for conservation of resources and protection against storm hazards, titled "Coastal Environmental Management". The six objectives recommended in this manual for communities to consider in developing "management policies" are:
1. Manage coastal watersheds for least alteration of natural patterns of storm water runoff. PA1 2. Preserve ecologically vital areas, such as dunes, coral reefs, wetlands, and edgezones (borders of distinctive vegetation between different areas-e.g. between wetlands and floodlands). PA1 3. Preserve the integrity of coastal geologic protective structures. PA1 4. Protect the configuration of coastal water basins against adverse alteration. PA1 5. Protect coastal waters from pollution. PA1 6. Restore damaged environments.
Heeding these recommendations recommend three separate designs of marine structures to be proposed herewith to preserve indirectly the integrity of geological and architectural coastal structures by safeguarding the nearshore zone (the submerged beach extending seaward as far as the force of waves reaches to the bottom) by making it nourish itself with sand utilizing a natural technique. To accomplish this, the theorem cited by Mr. Willard Bascom in his book, "Waves and Beaches" is put into practice. This practice is set forth by the statement that sand set in motion by wave caused turbulence will settle out wherever a protective structure reduces wave action. This assumption has been actually proven in nature on the island of Curacao, Netherlands-Antilles, in the Caribbean.
The proposed structures will not only add sand to the nearshore zone, but will also help reduce the severity of storm surges and flooding. This is accomplished in the same manner mangrove swamps and coral reefs are credited with saving the shoreline but in a more organized way without hiatuses.
Accordingly, there is a need for protective structures and assemblies mounted offshore which are designed, disposed and configured to reduce the wave energy by refraction (in marine terms meaning bending). Waves moving into a preferred structure or barrier assembly will also slow down by the friction caused by the obstacles course they are put through and that between the water particles reciprocally. Though part of the slowing down process will be caused by reflection, the utmost care is taken in the design of a preferred structure in order to offer the least resistance to the incoming waves. The powerful breakers, holding sand in suspension, get stripped of most of their energy after passing such a preferred barrier assembly and will release and add the suspended sand into the nearshore zone. With this action, the much feared erosion will be reversed and it will be a matter of time for the nearshore zone to silt up, sweep up enough sand to build dunes which will integrate coastal geologic protective structures.
The aforementioned prior art structures which are manmade are generally representative in the U.S. Pat. No. 4,647,290 to Grooms. Grooms recognizes that many and various techniques have heretofore been employed in conjunction with tidal waters, particularly along the coastline to attempt to cause sand carried by the water to settle therefrom during wave movement and thus achieve accretion. To date, such efforts have not met with any significant success. The Grooms' invention is not easily adaptable for large scale operations. It includes moving parts which make it vulnerable and costly from an operation and maintenance standpoint. The land accretion apparatus proposed by Grooms comprises a base support having a flexible barrier secured thereto. Apart from its operation, the following can be said of the flexible vertical barrier, which represents the most important part of the invention. The existence of a manmade material that can survive for a long constant back and forth bending motion brought about by the continuous wave action is questionable.